The present invention relates to a device for correcting a focus error signal obtained from an output of an optical pickup.
The optical pickup used in recordation and reproduction of an optical disc includes a light emitting element, an objective lens for collecting a light projected from the light emitting element on the optical disc, and a light receiving unit for receiving the light reflected by the optical disc. A focus error signal and a tracking error signal are detected based on an output of the light receiving unit, where focus control and tracking control by a servo are performed based on the respective signal.
Japanese Laid-Open Patent Publication No. 9-330522 discloses an optical disc device including a plurality of light receiving elements arranged in a planar form, where the device reads information recorded on the optical disc using a zero-dimensional light diffracted by a hologram, and detects the focus error signal and the tracking error signal using a ± one-dimensional light. In this document, a plurality of light receiving elements for detecting the focus error signal based on + one-dimensional light and a plurality of light receiving elements for detecting the tracking error signal based on − one-dimensional light are arranged on both sides of an optical spot position of a zero-dimensional light. Furthermore, the relevant document discloses a technique of accurately detecting out-of-focus even if an unnecessary zero-dimensional light has entered the light receiving elements by averaging a reflected light amount signal and comparing the same with a predetermined threshold value.
However, in the device described in this document, since the + one-dimensional light and the − one-dimensional light are used to detect the focus error signal and the tracking error signal the position of the light receiving element must be set accurately with respect to the respective one-dimensional light, which makes positional accuracy difficult to obtain. Thus, variation occurs in the detected signals and high accuracy servo control becomes difficult to perform. Furthermore, in the present document, a circuit for averaging the reflected light amount signal is required to remove the influence of stray light, which makes the circuit configuration complicating and leads to increase in cost.
Japanese Laid-Open Patent Publication No. 7-134831 discloses a technique of arranging an ambient light receiving region in the vicinity of a signal detection light receiving region of an optical detector in the optical pickup and calculating the difference between a signal obtained at the signal detection light receiving region and a signal obtained at the ambient light receiving region to remove a DC offset of the servo signal generated by the stray light. However, in the device described in this document, the ambient light receiving region must be arranged in addition to the signal detection light receiving region, which increases the surface area of the light receiving unit thereby inhibiting miniaturization of the optical pickup and increasing the cost.
Japanese Laid-Open Patent Publication No. 8-335323 discloses a technique of adjusting respective output balances of four light receiving cells configuring the light receiving element with a variable gain amplifier to remove a leakage signal of the track that mixes with the focus error signal, and stabilize the focus control. However, the arrangement of the light receiving elements in this document differs from the arrangement of the light receiving elements of the present invention to be hereinafter described, and the means for removing the leakage signal is completely different from that of the present invention.
Japanese Laid-Open Patent Publication No. 10-83541 discloses a technique of calculating the difference and the sum of the signal retrieved from a divided light receiving surface at each light receiving unit in which a light receiving surface is divided in half, equalizing a level of the difference signal of each light receiving unit with a respective sum signal, and combining each difference signal to generate the focus error signal to remove offset caused by an unbalance in amount of light of the divided light and variance in light receiving sensitivity at the light receiving unit. However, this document does not disclose countermeasures for the stray light and the arrangement of the light receiving elements is different from the arrangement of the light receiving elements of the present invention.